An acrylonitrile-butadiene-styrene resin (hereinafter, “ABS resin”) is a resin which is widely used in electric/electronic products, automobile components, and general goods due to excellent impact resistance, mechanical strength, surface properties, and processability.
However, since an ABS resin contains chemically unstable double bonds in a rubber component of the resin, the rubber component is likely to be aged by UV light. Such an ABS resin can suffer from relatively severe discoloration and deterioration in properties over time when left outdoors due to poor weatherability and light resistance and thus is unsuitable for outdoor use. In order to solve this problem, there has been proposed a method in which a molded article produced using the ABS resin is subjected to post-processing such as painting and plating, or a large amount of UV stabilizer is added when the ABS resin is subjected to extrusion. However, the former has shortcomings of complex processes and high defect rate, and the latter has problems of increased manufacturing costs and poor long-term weatherability.
In order to overcome such a problem of the ABS resin, various resins known to have good weatherability are used instead of the ABS resin. Particularly, an acrylate-styrene-acrylonitrile resin (hereinafter, “ASA resin”) is most widely used. Such an ASA resin has good properties in terms of weatherability, light resistance, chemical resistance, and heat resistance and thus is suitable for outdoor exterior materials that are exposed to sunlight for a long time, such as a material for outdoor electric/electronic products, an automotive exterior material, and a construction material.
Particularly, the ASA resin used as an automotive exterior material requires excellent colorability and heat resistance to provide a beautiful appearance with a black-based color.
Conventionally, an α-methyl styrene-based matrix SAN resin is generally used to improve heat resistance of the ASA resin. However, despite having good heat resistance, a copolymer of a vinyl cyanide compound and an α-methyl styrene compound used to provide heat resistance has high gas emissions causing deterioration in injection stability and problems in terms of appearance, such as deterioration in gloss, and can cause reduction in colorability, since the original color thereof is yellow.
In order to solve this problem, a method for improving colorability of a base resin by adjusting particle diameter of g-ABS or for improving colorability by adding an additive for facilitating dispersion of a pigment has been studied.
However, such a method of adjusting properties of a base resin has a limitation in improving colorability to a desired level and has a problem of reduction in heat resistance.
Korean Patent Publication No. 10-2013-0075812 (Patent Document 1) discloses an ASA resin composition which includes an acrylic graft copolymer, two vinyl cyanide-aromatic vinyl copolymers having different molecular weights, and an α-methyl styrene-based terpolymer and thus exhibits excellent properties in terms of impact strength, weatherability, and discoloration resistance at high temperature. However, such an ASA resin composition exhibits poor pigment-colorability and insufficient heat resistance.